The invention disclosed herein relates generally to keyboard apparatus, and more particularly to simplified construction of a keyboard in which the key tops define a surface of concave profile.
It is known that arranging the keys on a keyboard so that the key tops define a surface of concave profile provides ergonometric advantages. Specifically, arranging rows of key tops in a concave surface of proper radius about an axis decreases operator fatigue and aids in increasing operator speed and length of time of effective performance.
Various keyboard designs are known which provide the desired key top arrangement profile. In one such design, the structure in which the keys are carried is basically planar. The stem length and cap configuration for each key are selected as a function of the location of the key on the keyboard. This design has the disadvantage that keys having a variety of different stem lengths and cap configurations must be produced, and care must be used in assembly to insure that the proper key parts are used at each location.
The foregoing disadvantage is avoided in another design in which a rigid key mounting structure is preformed with the proper curvature. In such a design, keys of identical configuration can be used at all locations. However, such a design essentially requires that a key mounting structure be formed by a process and of materials other than molded plastic. Molding of a unitary rigid curved key holder plate is not feasible since a curved configuration and radially aligned key guide apertures preclude formation by a simple conventional mold.
A rigid curved mounting plate may be formed of sheet metal. However, with such construction, the mounting plate must generally be fitted with key guides, which is disadvantageous since extra parts and assembly steps are required. In addition, metal construction weighs more and is more expensive than construction of plastic materials.
U.S. Pat. No. 4,528,428 issued to H. Gotoh et al. on July 9, 1985 and 4,560,844 and 4,560,845 issued to T. Takamura et al on Dec. 24, 1985 disclose yet another curved keyboard design in which a flexible key holding structure is molded in planar form with integral key guide apertures. The key holding structure is then clamped to a first housing portion in a desired curved configuration by a rigid retainer plate. A mating housing portion is configured to provide additional support in maintaining the key holding structure in the desired configuration.
The key holding structure may be provided with longitudinal grooves or series of aligned slots between rows of keys for increasing flexibility of the structure transverse to the rows. It is also disclosed that the grooves may be formed of greater depth toward the outer edges of the structure to obtain desired deformation of the structure.
Although this arrangement is relatively simple and inexpensive, it requires a rigid curved retainer plate and individual fastening of the circuit board and the retainer plate to the first housing portion, and then assembly with a second housing portion to provide added support for maintaining the desired curvature.
Competitive pressures in the market place continue to dictate keyboard cost reductions. This necessitates fewer and more easily assembled parts. The applicant has devised a unique design fabricated entirely of inexpensive lightweight plastic parts in which the parts count is minimized and assembly is easily accomplished by snapping the parts together without any requirement for separate fasteners or fastening procedures.